This invention relates generally to electroplating apparatus, and more specifically, relates to apparatus useful in selective electroplating of extremely narrow stripes or lines of precious or semi-precious metals onto lengths of metallic base stock.
In numerous applications relating to the fabrication of electronic components, connectors, circuit boards and the like, a requirement exists for electroplating or otherwise depositing onto a base metal such as copper, brass, or the like, a precious metal, notably gold, for the purpose of improving the electrical and wear characteristics of the base metal, at least at the portion thereof where electrical connections are to be effected. Gold is noteworthy for such purposes because of its excellent and uniform electrical interface properties, its relative unalterability, and its high solderability.
At one time, it was relatively common to provide gold electroplating over an entire surface of a base conductor or face of an electronic component such as a header or the like, even though only a very limited portion of the surface being plated was actually intended to receive the electrical connections. Especially, however, because of enormous increases in the cost of gold, commensurate efforts have been made in recent years, to devise apparatus and methods for electroplating the precious metal only onto those portions of the base material whereat the ultimate electrical connections are to be made. The savings which can result from the use of these selective electroplating techniques are relatively enormous.
In one particular type of method for fabricating electronic connectors, a continuous strip of a base material, such as copper, is subjected to a series of punching and forming operations, such that terminal connectors for electrical components are eventually formed toward what was originally the lateral edges of the base strip. For present purposes the important point to note, is that as one aspect of fabrication methods of this type, the continuous metal strip, prior to the punching and forming operations, preferably has deposited thereupon longitudinally extending stripes of a precious metal such as gold. These gold stripes can, for example, extend along the lateral portions of the metal strip, or one or more such stripes can extend longitudinally at positions displaced from the lateral edges. Ultimately, these stripes (or lines) will define the electrical connection areas in the devices which are fabricated from the metal base strip.
It of course, again will be recognized, that one could in principle, plate the entire strip of base stock or one face thereof, etc.; but the consequent use of precious gold would be enormously expensive and wasteful.
In the past, apparatus has been proposed and utilized for achieving results of the type above discussed. For example, a line plating machine is disclosed in U.S. Pat. No. 3,819,502 to Meuldijk et al. Devices of this type usually involve the use of a rotating wheel or the like, which wheel is provided with a circumferentially extending slit through which the electroplating solution is fed from the interior of the wheel. The metal base strip passes about and is carried by the wheel while a plating potential is applied, whereby the strip is wetted through the wheel slit to electrodeposit the desired line or stripe. A somewhat similar arrangement is disclosed in U.S. Pat. No. 3,539,490.
A further approach for electroplating one or more longitudinal metal stripes onto a metal band is described in Dutch patent application No. 7,118,141, which was opened for inspection on July 3, 1973. In this disclosure the band is pulled through a channel defined in a plenum chamber between fixedly spaced flat insulating strips, of which one strip contains apertures for passage of electrolyte. A potential is applied between the band and a spaced anode whereby plating tends to occur in striped zones underlying the apertures. Since the band must move with respect to both spaced insulating strips and since both such strips are fixedly spaced, it is virtually impossible to maintain a fluid-tight seal between the apertured strip and the moving band, in consequence of which it is extremely difficult to maintain definition of the electroplated stripes.
The prior art methods, such as those mentioned above, have been found to be useful, and indeed to reduce the amount of gold which would otherwise have to be electroplated. However, in no known instance have these devices been capable of reducing the width of the line or stripe electrodeposited upon the base strip below about 60 mils. Further, the definition of the stripes has been less than adequate, and certainly less than desired. Indeed, production runs effected with commonly available machines indicate that the best tolerance achievable with non-indexing machines (indexing machines are described in the prior art such as U.S. Pat. Nos. 3,723,283 and 3,977,957), is in the range of 10 to 20 mils. In most cases, the location of a strip can be held within 1 mil or below.
The inability of these prior art devices to hold tolerances, necessitates depositing higher thickness of gold--in order to assure minimum required thicknesses, i.e., since the plated area has a tendency to vary. Furthermore, the inability to hold tolerances obliges one to plate larger surface areas than desired--to assure plating of the required thickness at the desired location.
Pursuant to the foregoing, it may be regarded as an object of the present invention, to provide apparatus for electroplating stripes or lines of precious metal or the like upon a base metal, which electrodeposited stripes or lines may in the practice of the invention be reduced to as little as 15 mils in width.
It is a further object of the invention to provide apparatus as aforesaid, wherein the quality of the electrodeposited material is extremely uniform, and of excellent density, thereby enabling superior electrical connections to be effected to same.
It is a yet further object of the present invention to provide apparatus of the above character, which enables ready variation in the positioning of electroplated lines upon base stock, which enables ready variation in the width of the lines or stripes thereby deposited, and which enables the simultaneous production of a plurality of continuously extending stripes on the base strip. strip.